A conventional printer P used generally for performing validation printing is of the kind shown, for example, in FIG. 1. When printing on card-type medium, such a printer is typically provided with a card feed mechanism, examples of which are shown in FIGS. 31 and 32.
FIG. 31 is a side view of a first example of a conventional card feed mechanism. In this type of card feed mechanism rotational energy of a card transport motor 6 is transferred to a card transport roller 301 via card transport power transmission gear train 10. A card presser roller 304 is axially mounted at one end of a card holder lever 303. Card holder lever 303 is pivotly mounted to the printer at pivot 303a and is biased by spring 305 in the standby position, as shown in the dotted lines. The other end of card holder lever 303 is coupled with a card presser plunger 302.
Card presser roller 304 is positioned in opposition to the card transport roller 301. The card presser roller 304, which is thus able to swing to attach to the card transport roller 301, is normally separated from the card transport roller 301 as shown by the dotted line while not printing, and is held to attach by the card presser plunger 302.
In operation, card 100 is inserted from above through the gap between print head 2 and platen 25, and then between card transport roller 301 and card presser roller 304 until it stops against card stop 306. This operation sets card 100 into the printer.
When current is supplied to card presser plunger 302 after inserting card 100, card holder lever 303 is rotated causing card presser roller 304 to move to the position indicated by the solid line against the tension of card holder lever spring 305. Card 100 is thus pressed between card transport roller 301 and card presser roller 304. Card transport motor 6 is then driven to transport card 100 to the specified position utilizing the frictional force between the two rollers 301, 304 and the card 100, and then printing is performed by print head 2.
After the printing one line, card transport motor 6 is again driven to advance card 100 to the next print position, and the card printing proceeds as described above. This cycle is repeated until the last line has been printed. When printing is finished, the current supply to card presser plunger 302 is interrupted, thus allowing card holder lever spring 305 to return card holder lever 303 and card presser roller 304 to the standby position (dotted line in FIG. 31). Card 100 can now be removed, and the card printing operation is completed.
FIG. 32 illustrates a simplified side view of a second example of a conventional card feed mechanism. In this example, only the feed mechanism is shown and the print mechanism is not shown. As shown therein, a card transport roller 323 is coupled to card transport ratchet wheel 327, which roller 324 is rotationally driven intermittently by card transport claw 328, via timing belt 325. Card presser roller 322 is coupled to a card presser plunger 321 and moves in response thereto. A spring 321a biases card presser plunger 321 so that card presser roller 322 is disposed in a position illustrated by the solid line. That is, card presser roller 322 is provided at a position opposite to card transport roller 323 and is lifted off card transport roller 323 by spring 321a during the non-printing or standby mode. When current is supplied to card presser plunger 321, card presser roller 322 is moved as indicated by the dot-dot-dash line so that card presser roller 322 is pressed against card transport roller 323.
In operation, card 100 is inserted into the printer from above. The presence of card 100 is detected by a detector (not shown) and current is then supplied to card presser plunger 321. As a result, card presser roller 322 moves in the direction of the arrow from the standby position indicated by the solid line to the position indicated by the dot-dot-dash line. Card 100 is thus held between card transport roller 323 and card presser roller 322. Card 100 is transported to the specified position for printing by the frictional contact of card 100 with card transport roller 323 and card presser roller 322.
During printing card 100 is fed to an appropriate position for printing by an intermittent feed technique using card transport claw 328 which is described briefly below. In this mechanism, card transport lever 329 is driven rotationally in the direction of arrow x and then in the opposite direction at a specified timing in accordance with a cam not shown in the figure. Card transport trigger lever 331 is engaged with card transport lever channel 329a during standby mode, thus preventing card transport lever 329 from turning in the direction of arrow z. When a "feed paper" command is received, current is supplied to card transport electromagnet 330, thus displacing card transport trigger lever 331 in the direction of arrow y to separate card transport trigger lever 331 from card transport lever channel 329a. Card transport lever 329 is controlled by the cam as it is turned in the direction of arrow z by the tension of card transport spring 332.
Card transport claw 328, which is provided on card transport lever 329 in a manner allowing claw 328 to pivot, drives card transport ratchet wheel 327 one step. Card transport lever 329 is then rotated in the direction of arrow x by the cam, and card transport trigger lever 331 drops into card transport lever channel 329a, thus locking card transport lever 329 and completing the card transport operation for card 100.
Such conventional card feed mechanisms have a number of disadvantages, problems and/or deficiencies as explained in detail hereinbelow.
More specifically, when multiple-layer printing forms are used, the top and bottom layers often slip out of position as the form is transported. This occurs because the rotational friction of the card presser roller is larger than the friction between the layers of the form, thus making it very difficult or impossible to print at the specified printing position throughout the layers.
The inventors have also observed that it appears to be impossible to eliminate a non-printing area in the vicinity of the top or bottom edge of the printing form. This non-printing area is a little wider than the radius of the card transport roller if the card transport roller is provided under or upper the print head. Though the problem can be solved by a structure which has two card transport means at both under and upper area of the print head, the structure is not suitable for POS and ECR printers because of its large size and high cost.
It is difficult to reduce overall printer assembly size because a large power supply is required to supply sufficient electrical power for the card presser plunger to generate sufficient force for the card presser roller to hold the card without slipping between the card and the rollers when the card is pulled by hand or other external force. Because of this factor also, such conventional mechanisms are not suitable for POS and ECR printers.
In the conventional printers as discussed above, printing forms or cards must be inserted to the card stop manually. In this arrangement it is very difficult to handle or print the cards or forms if the depth of the card stop is larger than the length of the cards or forms.
Additionally, the control circuit for the conventional printer is made more complex and expensive because it is necessary to control both the means for transporting the printing card and the card presser means for pressing the card to the card transport roller.
Finally, it is not possible to provide a combined card transport and presser unit because the card transport mechanism and the card presser mechanism are separated by the card. This increases the number of final assembly steps and unit cost.